Bump SixLabors.ImageSharp from 1.0.0-beta0007 to 2.1.7 in /18-CornellBoxWithSmoke#3

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dependabot/nuget/18-CornellBoxWithSmoke/SixLabors.ImageSharp-2.1.7Jorgemagic/RaytracingTheNextWeek:dependabot/nuget/18-CornellBoxWithSmoke/SixLabors.ImageSharp-2.1.7Copy head branch name to clipboard